PHOTOCHEMISTRY OF [RU(I)(IPR)(CO)(2)(IPR-DAB)] (IPR-DAB = N,N'-DIISOPROPYL-1,4-DIAZA-1,3-BUTADIENE) - HOMOLYSIS OF THE METAL ALKYL BOND FROM THE SIGMA(B)(RU-IPR)PI(ASTERISK) STATE - CRYSTAL STRUCTURE OF THE PHOTOPRODUCT [RU(I)(2)(CO)(2)(IPR-DAB)]

摘要

The complex [Ru(I)(iPr)(CO)(2)(iPr-DAB)] undergoes a very efficient photodecomposition (Phi = 1.2 at rt), whereas the corresponding complexes [Ru(I)(R)(CO)(2)(iPr-DAB)] (R = Me, Et) are photostable. ESR, using nitrosodurene and tBuNO as radical scavengers and time-resolved absorption spectroscopy showed that the primary photoprocess is a homolytic splitting of the ruthenium-isopropyl bond. This reaction most probably proceeds from the 3 sigma(b) pi* state of the complex, in which sigma(b) represents the (Ru-iPr) bonding orbital and pi* the lowest unoccupied orbital of the iPr-DAB Ligand. By using IR, UV-vis and H-1-NMR spectroscopy the bis-iodide complex [Ru(I)(2)(CO)(2)(iPr-DAB)] was identified as the final product. The single crystal X-ray structure of this photoproduct (C10H16N2O2I2Ru, M(r) = 551.1) was determined. The crystal is tetragonal, space group I4(1)/a, with unit cell dimensions a 11.552 (1), c = 24.489 (3) Angstrom, Z = 8. The structure refinement converged to R = 0.044 for 978 observed reflections. The very high quantum yields indicate that this photoproduct is formed by an electron transfer chain reaction of the radical [Ru(I)(CO)(2)(iPr-DAB)](.) with the parent complex. The temperature has a large influence on this reaction since its quantum yield decreases by a factor 3 when the temperature is lowered from 293 to 273 K. [References: 44]